Rheostatic braking is employed with a $4-$pole dc separately excited motor driving a load. The armature is wave wound and has $251$ conductors. The moment of inertia of the motor as well as the load is $350$ kg$.$m$2$$.$

The armature resistance is $0\mathrm{.}02\backslash$Omega $.$ Flux per pole is constant at $0\mathrm{.}02$ Wb$.$ Calculate the time taken to reduce the speed from $100$ rpm to $1$ rpm$.$ Armature current is $300$ A and constant until the entire external resistance is cut out.